Cooking appliance with steam generator

ABSTRACT

An apparatus and method for cooking with steam in a cooking appliance by forming the steam from atomized particles of water.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention generally relates to a cooking appliance thatincorporates a fluid into the cooking process.

2. Description of the Related Art

Conventional cooking appliances, such as ovens, for cooking food arewell known, and typically comprise a cabinet containing at least onehousing defining a cooking chamber and having a heating system forcooking food.

Some cooking appliances introduce water in the form of steam into thecooking chamber to facilitate the cooking process, such as in the bakingof bread and pastries. Such cooking appliances use a steam generatorthat changes the phase of water from liquid to steam by heating liquidwater. The steam is then introduced into the cooking chamber.

Heating the liquid water to such an extent, however, undesirablyconsumes a great deal of energy due to the high specific heat capacityof water created by hydrogen bonding between the water molecules.

SUMMARY OF THE INVENTION

The invention provides a more energy efficient way of using steam incooking appliance. In one aspect, the invention is a method of formingsteam in a cooking chamber of cooking appliance having a housingdefining the cooking chamber, comprising atomizing a liquid to form aplurality of particles of the liquid, introducing the particles into thecooking chamber, and maintaining the temperature of air in the cookingchamber at a temperature sufficient to change the phase of the particlesin the cooking chamber from liquid to gas to form the steam.

In another aspect, the invention is a cooking appliance comprising ahousing defining a cooking chamber, a heating element for heating thecooking chamber, an atomizer for generating particles of liquid andhaving an outlet for emitting the generated particles, with the outletdirectly connected to the cooking chamber such that the emittedparticles enter the cooking chamber without subsequent conditioning.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic view of a conventional oven with attached atomizerfor atomizing liquid water according to one embodiment of the invention.

FIG. 2 is a schematic view of the atomizer of FIG. 1.

FIG. 3 is a perspective view of the atomizer of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the figures, FIG. 1 schematically illustrates a cookingappliance in the form of a conventional oven 10 according to theinvention. The oven 10 comprises a cabinet 12 with an open-face cookingchamber 14 defined by a housing 16. The housing 16 comprises a pair ofspaced sides 17A, 17B joined by a top 17C, bottom 17D, and rear 17E. Adoor (not shown) selectively closes the cooking chamber 14. When thedoor is in the open position, a user can access the cooking chamber,while the door in the closed position prevents access to the cookingchamber 14 and seals the chamber 14 from the external environment. Theoven 10 further comprises an opening 21 located in the top of the oven10 adapted to receive liquid water.

The oven 10 further comprises a heating system for heating the cookingchamber or the food in the cooking chamber. As illustrated, the heatingsystem comprises at least one heating element 18, which is typicallyeither a gas or electric heating element. The heating element 18 can bemounted in any position suitable for heating the air in the cookingchamber 14, such as outside the cooking chamber 14 or at one of itssides, as is well-known in the oven art. Multiple heating elements 18can be mounted in any combination of positions.

The oven 10 may comprise a circulation system 20 that circulates air andsteam, when present, within the cooking chamber 14. The circulationsystem 20 can be any suitable system providing circulation, such as afan, and can be mounted in any suitable location of the cooking chamber14, such as in the rear.

While the cooking appliance is illustrated as a conventional oven, itcan be any type of cooking appliance that has a cooking chamber that isheated to cook the food.

An atomizer 22 is provided in the oven. The atomizer 22 generates waterparticles, which are then converted to steam that is used in the cookingchamber. The heat from the cooking chamber 14 is used to convert thewater particles to steam, which negates the need for the use of aseparate heating system for generating steam and reduces the overallenergy consumption of the oven when steam is used for cooking. Theatomizer 22 is preferably mounted within the cabinet 12 by any suitablemeans. A control 23 linked to the atomizer 22 is located on the top ofthe oven 10 and can be in the form of a button or switch.

A specific example of a suitable atomizer is illustrated in FIGS. 2 and3. For the purpose of describing the atomizer 22 of FIGS. 2 and 3, thedirections of inward, outward, forward, rearward, top, and bottom areused with respect to the orientation of the atomizer 22 in FIG. 2. Theatomizer 22 comprises an open-faced housing 24, which is closed by acover 40. The housing 24 defines an upper chamber 26 and lower chamber28. The upper chamber 26 is primarily for holding particles of water andthe lower chamber 28 is primarily a reservoir for water. The housing 24is preferably constructed of porcelain-coated steel, although it can bemade of any suitable material. The housing 24 comprises a pair of spacedside walls 30, 32, a top wall 34, bottom wall 36, and a back wall 37.The housing 24 further comprises a divider wall 38, a portion of whichis oriented approximately parallel to the top wall 34 and bottom wall36. The divider wall 38 is interposed between the side walls 30, 32, topwall 34, bottom wall 36, and back wall 37 in any suitable mannereffectively separating the upper chamber 26 from the lower chamber 28.

The cover 40 closes the open face of the housing and abuts the sidewalls 30, 32, top wall 34, bottom wall 36, and divider wall 38, and hasan orientation approximately parallel to the back wall 37. The cover 40can be fastened to the other elements of the housing 24 by any meanssuitable for creating an impermeable seal, such as by gluing orcaulking. An integral outlet 42 extends outwardly from the portion ofthe cover 40 defining the foremost face of the upper chamber 26. Theoutlet 42 fluidly connects to the cooking chamber 14.

A liquid water inlet 54 supplies water to the lower chamber 28. Theliquid inlet 54 can be configured for the unidirectional flow of liquidwater into the lower chamber 28. As illustrated, the inlet 54 isconnected to the opening 21 in the top of the oven 10 by a conduit 56(FIGS. 1 and 3) to permit direct filling by the user. However, othermethods and structures for supplying water to the conduit 56 may beused. For example, the conduit can be directly coupled to a householdwater supply. The conduit 56 can be coupled to the inlet 54 in anysuitable manner creating a watertight seal and enabling liquid waterflow to the inlet 54, such as by constructing the conduit 56 ofresilient tubing adapted to fit tightly around and retain the inlet 54.

A piezoelectric vibrator 44 is mounted to a portion of the bottom wall35 in which an opening 45 is formed. The piezoelectric vibrator 44vibrates at an ultrasonic frequency and transmits the vibrations intothe lower chamber 28 through the opening 45. In this way thepiezoelectric vibrator 44 can vibrate the water contained in the lowerchamber 28 and convert the water into particles.

A particle filter 48 is located between the lower chamber 28 and theupper chamber 26 and permits the transfer of water particles from thelower chamber 28 to the upper chamber 26. The particle filter 48 alsoretards the splashing of water from the lower chamber 28 into the upperchamber 26. As illustrated, the particle filter 48 comprises an opening50 in the divider wall 38 and which fluidly connects the upper chamber26 to the lower chamber 28. The particle filter 48 further comprises aparticle deflector 52 formed from the divider wall 38 by the opening 50.The particle deflector 52 is located above the opening 45 in the bottomwall 36. The particle filter 48 and its deflector 52 are formed as partof the divider wall 38 for convenience. The particle filter 48 can beseparate from the divider wall.

A fan 46 is mounted to a portion of the housing 24 and is in fluidcommunication with the lower chamber 28. The fan 46 can be any fanhaving a size and composition suitable for the purposes describedherein. The fan 46 is configured to draw air from outside the housing24, through the lower chamber 28, into the upper chamber 28, and out theoutlet 42 into the cooking chamber.

A brief description of the operation of the oven 10 with the atomizer 22will be helpful in understanding the invention. As the atomizer 22 doesnot contain its own heating source and relies upon the heated cookingchamber for converting the water particles into steam, the cookingchamber 14 should be heated prior to the introduction of water particlesfrom the atomized. For the water particles to be converted to steam inthe cooking chamber 14, the air in the cooking chamber 14 should beheated to a temperature appropriate for creating steam. This levelshould be at least 212° F. for the typical operating pressures of mostovens, which operate at atmospheric pressure, as this is the boilingtemperature of water. It has been found that a temperature higher thanthe boiling temperature is beneficial. The higher temperature should begreat enough such that all surfaces in the cooking chamber are at leastthe boiling temperature. In this way, any water particle that does notchange phase after entering the cooking chamber 14, will change phaseupon contact with the surfaces, which will prevent water from pooling onthe surfaces. Pooling water can be detrimental to many oven surfaces,such a ceramic, where it can lead to cracking. An air temperature of250° F. is typically great enough such that all surfaces within thecooking chamber 14 are at least 212° F.

Advantageously, cooking at a temperature of 250° F. requires littlepower relative to the total power available for cooking by the oven 10and is well below most cooking temperatures. Typically, foods are cookedat a temperature between 300° F. and 450° F., with a temperature ofapproximately 530° F. using the total power available and being themaximum possible temperature for cooking. As the majority of power usedto heat an oven escapes to the surrounding air as heat, cooking at alower temperature than normal reduces power consumption and,consequently, reduces energy costs. Additionally, studies have shownthat cooking at a lower temperature increases the nutritional value ofthe food being cooked.

Once the air in the cooking chamber 14 is heated to the appropriatetemperature, the controller 23 activates the atomizer 22. The controller23 can automatically activate the atomizer 22 or activate the atomizerin response to an input by the user. It is anticipated that a user willselect a cycle that requires steam, such as bread proofing or baking offish, and the controller 23 will take this input as a desire to generatesteam in accordance with the cooking cycle.

The controller can also control the volume of liquid water in the lowerchamber 28 by controller the valve in the inlet 54. Alternatively, thewater can be manually filled each time. It is not germane to theinvention how the water is supplied. There are many well known ways inwhich to supply water. The lower chamber 28 is filled with liquid waterto a level such that the piezoelectric vibrator 44 is covered by liquidwater, but the liquid water is not in contact with the particledeflector 52.

The piezoelectric vibrator 44 is actuated and vibrates to excite theliquid water molecules, resulting in the separation of a portion of theliquid water into liquid water particles in the space above the liquidwater. Larger liquid water particles are created above the center of thepiezoelectric vibrator 44 due to bubbling. These larger liquid waterparticles are prevented from moving into the upper chamber 26 by theparticle deflector 52 of the particle filter 48. Smaller liquid waterparticles created by the piezoelectric vibrator 44 have a tendency tospread outwardly above the piezoelectric vibrator 44. It is preferredthat the particles be of such a size that they are buoyant within theair. Buoyant particles are particles of this size will not immediatelyfall back into the water. Primarily, buoyant particles are of a sizethat they tend to stay in mixture with the air in the cooking chamberand evaporate before contacting any surface of the cooking chamber.

The fan 46 is activated by the controller to create a positive pressurein the lower chamber 28, which in turn creates a first pressure gradientin the atomizer 22. The first pressure gradient propels the smallerliquid water particles through the opening 50 of the particle filter 48in the divider wall 38. The smaller liquid water particles thenaccumulate in the upper chamber 26. Any condensation resulting from thecollision of liquid water particles in the upper chamber 26 is directedback down into the lower chamber 28 by the sloping of the divider wall38. The upper chamber 26 also has a positive pressure, which creates asecond pressure gradient. This second pressure gradient instigates themovement of the liquid water particles from the upper chamber 26 to theoutlet 42 of the cover 40. The liquid water particles move through theoutlet 42 and into the cooking chamber 14 of the oven 10.

Once in the cooking chamber 14, the liquid water particles are exposedto the heat of the air in the cooking chamber 14. Since the air in thecooking chamber has been heated to a sufficient temperature, it causesthe phase change of the water from liquid to gas, producing steam. Thesteam is then circulated throughout the cooking chamber along with theheated air using the circulation system 20.

The piezo type ultrasonic atomizer described and illustrated hereinprovides a cost-efficient means of cooking with steam. The atomizer isdesigned to for use with any conventional oven. The atomizer alsoeliminates the need for the separate heating element included in steamgenerating apparatuses. By using the heating element already present inthe oven to provide the energy needed to create steam, the piezo typeultrasonic atomizer greatly diminishes the additional costs associatedwith traditional steam-assisted cooking.

While the invention has been specifically described in connection withcertain specific embodiments thereof, it is to be understood that thisis by way of illustration and not of limitation. Reasonable variationand modification are possible within the scope of the forgoingdisclosure and drawings without departing from the spirit of theinvention which is defined in the appended claims.

1. A method of forming steam in a cooking chamber of an oven having ahousing having a plurality of surfaces defining the cooking chamber andan atomizer having an outlet fluidly coupled to the cooking chamber,comprising: atomizing a liquid to form a plurality of particles of theliquid that are of a size such that they are buoyant within air of theatomizer and do not immediately fall back into the liquid and stay inmixture with the air; introducing the buoyant particles into the cookingchamber by forming an air pressure gradient between the atomizer and thecooking chamber to propel the mixture of air and buoyant particles intothe cooking chamber; and maintaining a temperature of the air in thecooking chamber at a temperature greater than the liquid to gas phasechange temperature of the liquid and sufficient to maintain theplurality of surfaces at a temperature greater than the liquid to gasphase change temperature of the liquid, wherein the particles introducedinto the cooking chamber change phase from liquid to gas to form thesteam without the particles pooling on any surfaces of the housing. 2.The method of claim 1, wherein the particles are of a size such thateach of the particles completely changes phase from liquid to gas uponcontact with the housing defining the cooking chamber.
 3. The method ofclaim 2, wherein the particles are of a size such that each of theparticles completely changes phase from liquid to gas upon contact withthe air in the cooking chamber.
 4. The method of claim 3, wherein thetemperature of the air is maintained at a temperature such that thehousing is at least at a boiling point of the liquid.
 5. The method ofclaim 4, wherein in the liquid is water.
 6. The method of claim 1,wherein the particles are of a size such that each of the particlescompletely changes phase from liquid to gas upon contact with the air inthe cooking chamber.
 7. The method of claim 6, wherein the temperatureof the air is maintained at a temperature such that the housing is atleast at a boiling point of the liquid.
 8. The method of claim 1,wherein the atomizing of the liquid comprises vibrating the liquid. 9.The method of claim 8, wherein vibrating the liquid comprisesultrasonically vibrating the liquid.
 10. The method of claim 1, andfurther comprising forcing air into the particles to place them underpressure.
 11. The method of claim 1, wherein the temperature of the airis maintained at a temperature such that the housing is at least at aboiling point of the liquid.
 12. The method of claim 11, wherein thetemperature of the air is at least 212° F.
 13. The method of claim 12,wherein the temperature of the air is at least 250° F.